1. Field of the Invention
The present invention relates to medical leads, and more particularly to a temporary cardiac lead for pediatric applications and for temporary atrial and ventricular pacing and sensing during and after cardiac surgery.
2. Background Art
Temporary cardiac leads are commonly used for pacing and sensing in that they are generally less durable than permanent leads since extended flex life is not required. It is still critical, however, that the electrodes in the temporary leads be properly affixed to the heart tissue for proper transfer of electrical signals. This electrical contact must be established in a manner which permits convenient and safe removal of the temporary leads with minimal scarring or other side effects.
Several conventional techniques have been devised to improve lead fixation and to facilitate its removal. U.S. Pat. No. 4,341,226 which issued to Peters, which is assigned to Medtronic, Inc., and which is incorporated herein by reference, is an exemplary illustration of such conventional art. The Peters patent describes a temporary lead and a corresponding insertion tool. The electrode of the temporary lead is connected to a surgical thread which extends into a helically shaped coil. The coil has a circular cross section, and is disposed at a short distance from the electrode tip. A curved needle is attached to the surgical thread for insertion into the heart tissue.
In ventricular applications, the needle is pulled through the myocardium for bringing the electrode into contact with the heart. The coil is pre-stretched before positioning by applying tension to the needle. Thereafter, as soon as the pulling force is removed, the coil tends to resiliently resume its initial pre-stretched shape. This will cause the coil to capture the tissue and to anchor itself thereto, thereby fixing the lead into position relative to the heart.
The disengagement of the coil from the myocardium and the removal of the temporary lead is accomplished by applying a force to the proximal end of the lead. This will cause the coil to stretch axially and to disengage from the myocardial tissue.
Atrial applications of the temporary lead vary from the ventricular applications described above due to the thinness of the atrial wall. In order to prevent damage to the atrial tissue, two alternative techniques are generally used in conjunction with the temporary lead. The first technique is to position the lead in a small plica on the surface of the atrium, and to hold the plica folded by means of sutures. The alternative technique is to use a silicon rubber fixation disc instead of the atrial plica. The disc retains the lead and is sutured to the atrial wall. The disc is permanently affixed to the atrial wall, and is not removed with the temporary lead. Therefore, it would be beneficial, convenient and expeditious to design a new self-anchoring temporary which does not require supplemental holding means such as plicae or retention discs.
Medtronic, Inc. is marketing the temporary lead covered by the Peters patent as part number 6500. While this temporary lead has proven to be effective in many respects, it would be desirable to improve its design in order (1) to ameliorate the coil positioning property by reducing slippage between the coil and the myocardium; (2) to dispense with auxiliary accessories such as the silicon rubber discs, thereby facilitating the lead useability in both the atrium and the ventricle; (3) to reduce the lead size for pediatric applications; and (4) to permit convenient and safe removal of the temporary lead with minimal scarring or other side effects.
Other exemplary patents in the relevant field of the invention are: U.S. Pat. Nos. 3,485,247 and 3,516,412 issued to Ackerman; U.S. Pat. No. 3,244,174 issued to Wesbey et al.; U.S. Pat. No. 3,474,791 issued to Benton; and U.S. Pat. No. 4,144,889 issued to Tyers et al.
The conventional temporary leads described in these patents have not been completely satisfactory in securing safe affixation and removal. Safe affixation and removal of temporary leads are of particular importance in pediatric applications due to the thinness of the ventricular and atrial walls of the young patient's heart. Furthermore, complications can even evolve with adult and young patients, in that lead removal might result in cardiac tamponade.